This invention concerns an aqueous heat-curable coating substance in a polyester and acrylic resin base mixed with amine resin and neutralization agents, which may contain the usual paint additives, pigments, fillers and/or organic solvents. The aqueous coating substance can be used in the manufacture of coatings, particularly as a base coat in multilayer coatings, preferably as a clear varnish.
The construction of multilayer coatings is particularly well known in the automobile manufacturing sector, in which it is advantageous to apply a layer of clear varnish .wet on wet to a base coat following a brief drying period, whereupon the two are baked on together.
Aqueous base coats are described in the literature and used in practice. However, in practice such base coats are still provided with coatings of non-aqueous clear varnish. Although DE-PS 28 06 497 describes a multilayer coating with a cover coat of clear varnish in which this clear varnish may also be water-thinnable, examples of such water-thinnable clear varnishes are not cited. Polyester with a high molecular weight and high viscosity, which is dissolved in xylene and may be mixed with acrylate resins, is used to cover the base coat. Such varnishes have a high neutralization agent requirement and produce a high solvent emission during application.
DE-OS 37 12 442 describes a mixture of polyester-melamine resin adduct with acrylic resins. Again, high quantities of neutralization agent are required.
DE-OS 36 32 617 describes aqueous coating compounds in a base of highly viscous resins, for example polyester resins, in which resin particles, which may be acrylic resin, are dispersed. The resulting compounds are unstable and subject to rapid phase separation.
EP-A-0 206 072 describes filmogens in a base of acrylic polymer products manufactured in a thinning agent with a molecular weight of more than 200, which may be a polyester or other material. However, these filmogens cannot be used in aqueous systems.